There are a lot of unanswered questions about the ambitious project.

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Elon Musk's Boring Company is nearing completion of its first tunnel near SpaceX headquarters. In a Thursday evening Instagram post, the mogul showed off a fly-through video:

"Pending final regulatory approvals, we will be offering free rides to the public in a few months," Musk wrote. "As mentioned in prior posts, once fully operational (demo system rides will be free), the system will always give priority to pods for pedestrians & cyclists for less than the cost of a bus ticket."

It's not clear how far Musk plans to take his tunneling project. He certainly has an ambitious vision. In a March tweet, he wrote that "Boring Co urban loop system would have 1000’s of small stations the size of a single parking space that take you very close to your destination & blend seamlessly into the fabric of a city, rather than a small number of big stations like a subway."

Musk's team has also done some preliminary work on the electric sled that would carry people around in the system—he showed off a prototype of the technology last year.

At the same time, other details of Musk's vision are maddeningly vague. Initially, Musk envisioned the system as a faster way to move cars around the city. More recently, he has indicated that the system would give priority to pedestrians and cyclists, making it sound more like a conventional subway.

But it's not obvious that tunneling technology, per se, is the big obstacle to building more extensive subway networks. It was relatively easy to get permission to tunnel under the Baltimore-Maryland Parkway because that land was owned by the state of Maryland and didn't have a lot underground. But an urban subway system needs the right to tunnel under thousands of pieces of privately owned land. It needs to avoid damaging underground pipes and wires, and stations need access to the surface.

The planning, negotiations, environmental reviews, and litigation required to get all the necessary permissions account for a large share of the costs of any ambitious transportation project. Musk undeniably has some experience negotiating with government agencies—after all, he convinced NASA to take a chance on SpaceX rockets. But so far there hasn't been much sign that he's actually laying the groundwork that would be necessary to build a functional transportation network in California, Maryland, Illinois, or anywhere else.

Correction: I misread an LA Times story and got two tunnels confused. As a result, I described this as a 2.7-mile tunnel in West Los Angeles, when in fact that's a different tunnel that has been proposed but hasn't been constructed yet. This tunnel, in contrast, is located around SpaceX headquarters in Hawthorne. Musk hasn't revealed its exact length, but the company submitted a proposal for a 2-mile tunnel at the site last year. We regret the error.

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Density is going to be a huge problem for this idea:- For not-particularly dense cities you need very large tunnels to build a system worth using. This is very expensive. - For dense cities having a lot of small stations is inefficient as land is more expensive. More population also means crowded stations. - Elevators for cars or passengers ingress/egress have a capacity way smaller than ramps/scalators. - Throughput is going to be a problem as you need enough separation between sleds to allow them to stop without crashing in case of failures. This separation combined with the small size of the sleds is going to result in a very small passengers/hour/tunnel capacity.

Efficiency is going to be a huge problem. Musk's idea are cars that hold 8 to 16 passengers and can travel at 150mph. For comparison a typical subway train holds 180 people with 10 cars at a max speed of 55mph. A Muskway system would need to load and move one pod every 8 to 10 seconds to match the efficiency of one subway train that runs every 15 minutes. Speed is great, but without a good capacity it's not a good solution for congested areas.

My guess is that the focus is less on disrupting the work of boring the tunnel but more on making the construction of adits easier. They'll need some huge openings in the tunnel lining if they're going to have 'a main artery tunnel with side tunnels for entry/exit' (quote from the Boring Company FAQ).

When you build a bolted tunnel lining like theirs, the circular shape of each ring is self-supporting. Everything's fine until you have to create an opening in the lining. My tunnelling colleagues freak out at the openings we request for escape cross-passages & vent adits. I've never managed to convince them to cut out part of more than one ring, and they usually insist on a couple of complete rings next to the weakened ring to support it. Large adits for ventilation usually end up as two, three or four smaller adits spaced several rings apart. It's often easier to build the shaft first, hollow out an adit that's larger than the tunnel diameter then drive the TBM through it (once the TBM is far enough away you demolish the rings inside the adit to create the junction).

The challenge I see is not in reducing the cost of building a length of self-supporting bored tunnel - the challenge is how to build a network of interconnecting side tunnels that don't collapse when you cut through the lining of the artery tunnel. It'll be interesting to see how they address that.

At the same time, other details of Musk's vision are maddeningly vague. Initially, Musk envisioned the system as a faster way to move cars around the city. More recently, he has indicated that the system would give priority to pedestrians and cyclists, making it sound more like a conventional subway.

The man needs a mental lowpass filter, frankly. Conceive a thing, study the thing, decide on the thing, do the thing.

If you put too many irons in the fire, you run the risk of them getting cold. Is he writing Boring Company press releases from his cot on the Tesla production line?

the system will always give priority to pods for pedestrians & cyclists for less than the cost of a bus ticket.

So, it's a subway?

Not exactly. I mean it is in the terms of it is a transportation system underground, but instead of there being trains that take you from point A to point B they are small individual 'cars' (ie subway cars) taking people where they need to go:

So instead of having a single train on a loop you can have multiple smaller vehicles using the same tracks to take people directly where they want to go with a minimum of stops in between.

Similar to the limit in which a property owner has rights above land, I’d gather there’s a similar limit to go under. The deepest Tube station is 192ft, and one in Kiev at 346ft. Surely there’s a limit where permission is no longer required from said property owner, rather the state.

It seems like his proposed system has more points of failure than a traditional subway train system. I appreciate the idea that I could drive my car into and out of this system to continue my journey. But every single sled has to function or else the whole tunnel comes to a stop.

Similar to the limit in which a property owner has rights above land, I’d gather there’s a similar limit to go under. The deepest Tube station is 192ft, and one in Kiev at 346ft. Surely there’s a limit where permission is no longer required from said property owner, rather the state.

Unlike airspace which can't really harm the property until its very low, underground space can always harm the property above it. So yes liability is a big deal when you dig under someone else's property.

Similar to the limit in which a property owner has rights above land, I’d gather there’s a similar limit to go under. The deepest Tube station is 192ft, and one in Kiev at 346ft. Surely there’s a limit where permission is no longer required from said property owner, rather the state.

Nope. In the US property rights extend to the center of the Earth in theory, and in practice as deep as you can dig or drill. This has long been settled law due to mining and the oil and gas industry.

Governments can force a right of way through your property by eminent domain, but they have to pay for it. Private organizations can't force property owners to do anything.

"LA officials waived environmental reviews to give Musk a chance to test out the technology." And there it is. There is nothing inherent in digging a subway that makes it astronomically expensive. But once you factor in the environmental reviews, the inevitable lawsuits, etc., it adds up. I'm a lefty environmentalist so I support the reviews, but there's a cost to be paid for them.

As to the lawsuits, well, they're frankly ridiculous. If anyone is curious, look up the saga of getting the Expo Line built here in LA-- and that was an above-ground light rail trolley. You can imagine what getting an underground subway built takes (hell the Beverly Hills Unified School District recently filed another lawsuit against the Purple Line, even though they had yet to prevail in any of the previous ones).

So, good luck Elon. You're going to need it.

EDIT: oh, wanted to add, Metro already owned the right-of-way for the Expo Line! And they still had to contend with lawsuit after lawsuit even after the environmental review came through.

Similar to the limit in which a property owner has rights above land, I’d gather there’s a similar limit to go under. The deepest Tube station is 192ft, and one in Kiev at 346ft. Surely there’s a limit where permission is no longer required from said property owner, rather the state.

Interesting question. A skyscraper can have a foundation that's 170ft deep. I think most subways try to avoid being directly below large buildings because of the engineering hassles.

Similar to the limit in which a property owner has rights above land, I’d gather there’s a similar limit to go under. The deepest Tube station is 192ft, and one in Kiev at 346ft. Surely there’s a limit where permission is no longer required from said property owner, rather the state.

Probably, but you also probably start running into the issue of having to tunnel through bedrock, rather than softer soils. Plus, the deeper you go, the more inconvenient it is to get to. If Musk envisions this as almost as easy as hopping on a bus, having to take an elevator ride to the center of the earth will make it a bit slower.

Instead of tunneling long continuous subway tunnels, maybe he could just create multiple, shorter 2-3 mile tunnels across the city, like airport motorized walk-ways that have a gap at a group of gates? That way he can avoid tunneling through the most complicated areas, and pick off where there's less obstacles and still have some sort of patch-work system.

Ultimately I'm sure it will lead to an underground lair inside a volcano.

My guess is Elon wants to connect the Hawthorne plant with the BFR site at the Port of Los Angeles. The Port of LA, in turn, would be happy to have a way of getting cargo out of the port without using so many trucks.

The video clearly highlights a single-track system; does Musk intend this to be a one-way route that switches directions with the prevailing flow of rush hour traffic?

Also, don't most cyclists choose that method of travel to enjoy the outdoors while getting some exercise? In which case, going underground and standing next to your bicycle on an electric sled would seem to defeat the purpose.

On the other hand, one can imagine LA traffic jams could have driven people who wouldn't normally bicycle onto two wheels out of necessity, in which case those commuters may welcome a respite from the stoplight slog.

A series of tunnels would move people much slower than a large system of roads. Cool tube stuff doesn't equal intelligent logistic urban planning. I love the concept but the only way this will help anyone is at a massive premium for specific transport. Especially the system targeted for cars. Even at ten times the speed imagine two highways in a district (Los Angeles) with 17 million people moving perpetually. It's flashy but it's not efficient.

Instead of wasting massive resources, maybe population density can take a chill pill, seriously.

It seems like his proposed system has more points of failure than a traditional subway train system. I appreciate the idea that I could drive my car into and out of this system to continue my journey. But every single sled has to function or else the whole tunnel comes to a stop.

Trains concentrate propulsion into fewer points of failure.

The difference will be in travel times. With a subway, the train is shared by a large number of people, and thus it must make unnecessary stops ("unnecessary" for everyone who doesn't use that stop).

With small vehicles, you group up just the people who are all ready to go to the same destination and you take them there with no intermediate stops. This has a profound effect on average speed.

There are a few other design differences you need to make vs a subway to make this practical. The pods don't block the line at the station. You can lay out your system with more loops, so as to cover an area rater than just a "transit corridor".

The general concept was thought of decades ago (50's or 60's) and is often called "Personal Rapid Transit" or PRT. It's been debated in various corners of the internet for almost as long. Musk's is far from the first PRT system to be built, but it's certainly the highest profile, and (IMO) the most likely to genuinely succeed.

The video clearly highlights a single-track system; does Musk intend this to be a one-way route that switches directions with the prevailing flow of rush hour traffic?

Also, don't most cyclists choose that method of travel to enjoy the outdoors while getting some exercise? In which case, going underground and standing next to your bicycle on an electric sled would seem to defeat the purpose.

On the other hand, one can imagine LA traffic jams could have driven people who wouldn't normally bicycle onto two wheels out of necessity, in which case those commuters may welcome a respite from the stoplight slog.

Yeah I wouldn't (and don't) bike on most of the arterial streets in LA (like Sepulveda). There's just not enough protection for cyclists. People do it, but it's rare.

It seems like his proposed system has more points of failure than a traditional subway train system. I appreciate the idea that I could drive my car into and out of this system to continue my journey. But every single sled has to function or else the whole tunnel comes to a stop.

Trains concentrate propulsion into fewer points of failure.

The difference will be in travel times. With a subway, the train is shared by a large number of people, and thus it must make unnecessary stops ("unnecessary" for everyone who doesn't use that stop).

With small vehicles, you group up just the people who are all ready to go to the same destination and you take them there with no intermediate stops. This has a profound effect on average speed.

There are a few other design differences you need to make vs a subway to make this practical. The pods don't block the line at the station. You can lay out your system with more loops, so as to cover an area rater than just a "transit corridor".

The general concept was thought of decades ago (50's or 60's) and is often called "Personal Rapid Transit" or PRT. It's been debated in various corners of the internet for almost as long. Musk's is far from the first PRT system to be built, but it's certainly the highest profile, and (IMO) the most likely to genuinely succeed.

This is an expensive an inefficient solution imagined by a wealthy person. On a medium term basis free helicopters would be more efficient at scale for at least a series of years. Tunneling is laborious and expensive and the turn needs to be made at some point. I love the ambition of it all but it doesn't pan out as it's described. Especially in a region like Los Angeles which is why a subway system is already not commonplace.

Density is going to be a huge problem for this idea:- For not-particularly dense cities you need very large tunnels to build a system worth using. This is very expensive. - For dense cities having a lot of small stations is inefficient as land is more expensive. More population also means crowded stations. - Elevators for cars or passengers ingress/egress have a capacity way smaller than ramps/scalators. - Throughput is going to be a problem as you need enough separation between sleds to allow them to stop without crashing in case of failures. This separation combined with the small size of the sleds is going to result in a very small passengers/hour/tunnel capacity.

The video clearly highlights a single-track system; does Musk intend this to be a one-way route that switches directions with the prevailing flow of rush hour traffic?

A viable system will need the equivalent of three tracks. One in each direction, plus a bypass for stopped pods at stations, or a siding for the pods to pull in to. In case a pod fails mid-tunnel you would want access for a "tow truck" or some way to get it out of the main tunnel so other pods can run.

it seems very unlikely that Musk is really thinking of this as a mass transit system, despite his pronouncements that pedestrians and cyclists will be given priority at less than the price of a bus ticket.this is a personal transit system dreamed up by a rich guy who was pissed off about being personally inconvenienced by getting stuck in traffic and intended to be used by other rich guys.so, the issues of scalability etc. aren't crucial. By design.

This is an expensive an inefficient solution imagined by a wealthy person. On a medium term basis free helicopters would be more efficient at scale for at least a series of years. Tunneling is laborious and expensive and the turn needs to be made at some point. I love the ambition of it all but it doesn't pan out as it's described. Especially in a region like Los Angeles which is why a subway system is already not commonplace.

Luckily, Musk doesn't need your approval to waste his money.

Really though, he's betting that he can make tunnelling relatively cheap, at least compared to the status quo. Complete nonsense, of course, right up there with the absurd thought that you could ever make spaceflight cheap.

Density is going to be a huge problem for this idea:- For not-particularly dense cities you need very large tunnels to build a system worth using. This is very expensive. - For dense cities having a lot of small stations is inefficient as land is more expensive. More population also means crowded stations. - Elevators for cars or passengers ingress/egress have a capacity way smaller than ramps/scalators. - Throughput is going to be a problem as you need enough separation between sleds to allow them to stop without crashing in case of failures. This separation combined with the small size of the sleds is going to result in a very small passengers/hour/tunnel capacity.

Especially in regions specified this is a solution to suit Musk himself or other people of high wealth. A tunnel doesn't beat a road and it would take thousands in a city with so much geographic disparity as LA. It only makes sense as a premium product for wealthy individuals. It's an exciting concept but it's not based in reality. An urban road cost around $2-3m/mile and a tunnel costs around $1billion/mile ^1. Expand that to a large system or roadways. Even with high improvements in efficiency it's flat out silly. ^1 https://www.teslarati.com/boring-compan ... l-digging/

Similar to the limit in which a property owner has rights above land, I’d gather there’s a similar limit to go under. The deepest Tube station is 192ft, and one in Kiev at 346ft. Surely there’s a limit where permission is no longer required from said property owner, rather the state.

Probably, but you also probably start running into the issue of having to tunnel through bedrock, rather than softer soils. Plus, the deeper you go, the more inconvenient it is to get to. If Musk envisions this as almost as easy as hopping on a bus, having to take an elevator ride to the center of the earth will make it a bit slower.

Los Angeles is a mess of absurdly deep sediment basins (the one that bottoms out just to the south east of central LA bottoms out at about 6 *miles*) and faultlines. You're not going to have too much trouble with bedrock, which may be one of the reasons Musk is experimenting there. http://scecinfo.usc.edu/phase3/basinmap.html